What’s the Harm of Hanging On to Weak Dietary Advice?

Two recent articles have us thinking about the harm that might come from hanging on to weak dietary advice. One is all about salt. The other is about dairy fat. But underneath it all is core problem. Some of the dietary advice taken as gospel is grounded in associations and suppositions. It never goes through rigorous, scientific testing.

Thin Evidence for Salt Recommendations

In the New York Times, Professor Aaron Carroll tells us that the advice to cut salt for folks with heart failure stands on a paper-thin evidence base. A new systematic review made it plain. Most of the studies on sodium for heart failure – 99.7 percent – were of such poor quality that they provided no evidence for the review. That left only nine studies with a total of only 479 patients. None of them involved more than a hundred patients. All of them had a moderate or high risk of bias.

So we need better evidence, which may come from two large ongoing trials. However, Aaron takes issue with standing firm with advice to cut sodium while we wait for real scientific answers:

Until then, some will argue that there’s little harm from these recommendations, so why not continue them? One reason to stop them is that there’s a risk of emphasizing salt avoidance at the expense of other – potentially more useful – diet measures, when we really don’t know what’s best.

Wobbly Warnings About Dairy Fat

We’ve written many times (most recently here) about the zombie guidance to avoid dairy fat. JAMA recently published yet another report on the intense debate. The argument against advice to avoid dairy fat is simple. The evidence just isn’t there for making strong recommendations.

On the other side of the argument, it boils down to this. It’s already there in the dietary guidelines. Sure, we need more evidence. But we don’t have sufficient evidence to change the guidelines, either. So let’s just keep doing what we’ve been doing and change the subject. We can’t have people questioning our dietary guidelines.

How About Some Real Science?

In the New York Times, Siddhartha Mukherjee offers a modest proposal:

Rather than relying on received knowledge, or on presumed ideas, we might examine our diet molecule by molecule, and trial by trial, probing the aspects of food that incite or treat particular diseases, for particular humans, with particular genetic attributes. In the age of molecular therapeutics, perhaps we might need to rethink diet, too, as a form of molecular therapy.

In other words, it’s time to really study the effects of dietary recommendations – both for maintaining health and coping with disease.

For folks deeply invested in the status quo, this is anathema. Clinical trials are for pharmaceuticals, they protest. For nutrition, they advocate vigorously for large, prospective cohort studies. The kind they do. That nasty drug-trial paradigm “cannot be readily translated for use in the nutritional sciences,” they tell us.

We disagree. Experimental methods are not a contrivance of the pharmaceutical industry. They are the bedrock of science. Mukherjee is right. It’s high time that we work harder to test our presumptions about nutrition. Suppostions and associations are not enough. “That’s what we’ve always recommended” is an insufficient justification for dietary guidance.

What’s the harm of hanging on to weak dietary advice? A house built on sand will wash away. Guidance without a strong foundation of evidence is nothing but a distraction.

Click here for the commentary on salt by Carroll, here for the JAMA viewpoint on dairy fat, and here for the essay by Mukherjee.

Still Life with Salt Tub, painting by Pieter Claesz / WikiArt

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December 18, 2018